The present invention relates to a method for manufacturing a semiconductor device; and, more particularly, to the method for manufacturing a ferroelectric random access memory (FeRAM) device to prevent the device from damage induced by a package process by applying an annealing process before the package process.
With the recent progress in film deposition techniques, applications of a nonvolatile memory cell using a ferroelectric thin film have increasingly been developed. This nonvolatile memory cell is a high-speed rewritable nonvolatile memory cell utilizing the high-speed polarization/inversion and the residual polarization of the ferroelectric capacitor thin film.
Therefore, a ferroelectric random access memory (FeRAM) where a capacitor thin film with ferroelectric properties such as strontium bismuth tantalate (SBT) and lead zirconate titanate (PZT) is increasingly used for a capacitor in place of a conventional silicon oxide film or a silicon nitride film, because it assures a low-voltage and high-speed performance, and does not require periodic refresh to prevent loss of information during standby intervals like a dynamic random access memory (DRAM).
Since a ferroelectric material has a dielectric constant ranging from hundreds to thousands value and stabilized residual polarization property at room temperature, it is being applied to the non-volatile memory device as the capacitor thin film. In case of employing the ferroelectric capacitor thin film in the non-volatile memory device, information data are stored by polarization of dipoles when an electric field is applied thereto. Even if the electric field is removed, the residual polarization remains so that the information data, i.e., xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d, can be stored.
However, there are reliability problems for utilizing FeRAM as a memory device despite the fact that FeRAM has several advantages as aforementioned. Generally, there are two kinds of reliability problems in FeRAM, one of which is a fatigue problem and the other is a retention problem. The fatigue problem is related to how many times it preserves the data during repeated reading out and writing of the data, and the retention problem is related to how long it preserves the stored data.
To address the reliability problem of fatigue, attempts are made to use iridium oxide (IrO2) or ruthenium oxide (RuO2) as an electrode instead of platinum (Pt) when PZT is used as the capacitor thin film. Meanwhile, in case of using SBT as the capacitor thin film, a Pt electrode can be still available which shows improved property against the fatigue problem. Thus, the reliability problem related to fatigue of the memory device has been overcome to a considerable degree, i.e., 1010xcx9c1013 cycles.
However, the second reliability problem of retention still remains as a serious matter. If the fabricated device is left alone for a long time after writing information data of xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d, a critical voltage is changed so that the stored data can hardly be read out with accuracy. In addition, if the device is exposed to high temperature for long time, the device characteristic is more deteriorated than in room temperature. For example, if a package process is carried out for the fabricated FeRAM device after a wafer level function test, the FeRAM experiences high thermal budget so that a pass rate of the device decreases eventually, because this package process is performed at high temperature for long time.
Especially, a post mold curing (PMC) process for curing the molding compound implicates the retention problem, where the process is carried out at 150xcx9c175xc2x0 C. for 5xcx9c6 hours.
In more detail, after completing the fabrication of the FeRAM device, the wafer level function test is carried out to identify the defective device. However, after this test, the memory cells have one of the data, xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d. This means that domains in the ferroelectric capacitor thin film are arrayed in predetermined orientations to generate an electric field. Therefore, when the package process is carried out at high temperatures for a long time, providing that the domains are arrayed in the predetermined orientations, mobile defects easily move toward grain boundaries due to the electric field so that charge distributions at the grain boundaries get changed. This change of the charge distributions results in critical voltage shift, e.g., decrease or increase, and further this change brings a decrease of residual polarization, whereby the device eventually fails.
In other words, if the package process is performed after wafer level function test, the dipoles being oriented in the predetermined direction, the pass rate of the FeRAM device after the package process decreases more than that after the wafer level function test. Thus, the reliability problem of retention represents an obstacle for applying the FeRAM device as a memory device.
It is, therefore, an object of the present invention to provide a method for manufacturing a ferroelectric random access memory (FeRAM) device to prevent deterioration thereof by applying an annealing treatment.
In accordance with one aspect of the present invention, there is provided a method for manufacturing a ferroelectric random access memory (FeRAM) device, the method comprising the steps of: a) forming a unit die including a transistor and a capacitor on a semiconductor substrate; b) testing a wafer level function for the unit die; c) annealing the device above Curie temperature of ferroelectric material; and d) carrying out a package process for the device.